tolong menggunakan cara no 9 terimakasih ...

Kelas 8 Matematika
Bab Barisan dan Deret BIlangan

r = U2/U1
r = 9/18
r = 1/2

Un = 9/64
a . rⁿ⁻¹ = 9/64
18 . (1/2)ⁿ⁻¹ = 9/64
(1/2)ⁿ⁻¹ = 9/64 . 1/18
(1/2)ⁿ⁻¹ = 1/64 . 1/2
(1/2)ⁿ⁻¹ = 1/128
(1/2)ⁿ⁻¹ = (1/2)⁷
n - 1 = 7
n = 7 + 1
n = 8